1. Field of the Invention
The present invention relates to tendon tensioning anchor assemblies in general and to an apparatus for protecting from corrosion the exposed portions of the ends of a tendon held in a tendon tensioning anchor assembly in particular.
2. Description of Prior Art
Concrete structures, such as bridges, dams, buildings and the like, are frequently constructed using one or more reinforcing tendon pre- and/or post-tensioning anchor assemblies.
In a typical tendon tensioning anchor assembly there is provided a pair of spaced anchors for anchoring the ends of a tendon suspended therebetween. The tendon, particularly in a tendon post-tensioning anchor assembly installed in a concrete structure, is usually enclosed within a waterproof sheath to isolate the tendon from the surrounding concrete structure.
In the course of installing the tendon tensioning anchor assembly in a concrete structure, after stripping the waterproof sheath from a portion of both ends of the tendon to facilitate suspending the tendon between two spaced anchors, a hydraulic jack or the like is releasably attached to at least one of the exposed ends of the tendon for applying a predetermined amount of tension to the tendon. The sheath, within which the remainder of the tendon is enclosed isolates the tendon from the surrounding concrete and facilitates the movement of the tendon relative to the surrounding concrete. When the desired amount of tension is applied to the tendon, wedges, threaded nuts or the like forming a part of the anchors, are used to capture the tendon and, as the jack is removed from the tendon, to prevent its relaxation and hold it in its stressed condition.
Tendons within concrete structures may become exposed to corrosive elements, such as de-icing chemicals, sea water, brackish water, or spray from these sources, as well as salt air. If this should occur and the exposed portions of the tendon suffer corrosion, not only will the tendon be weakened due to the corrosion, but the resulting large volume of the byproducts of the corrosive reaction is often sufficient to fracture the surrounding structure. When the surrounding structure is fractured and additional corrosive elements come in contact with the tendon, premature failure of the tendon and deterioration of the structure will occur.
In U.S. Pat. No. 3,967,421 issued to Marcel Emile Duffossez on July 6, 1976, there is disclosed a bonded tendon anchor assembly comprising a plurality of tendons enclosed within a sheath. At one end thereof, the tendons are attached to a threaded tubular anchor assembly which is isolated from a surrounding concrete structure by a housing. At the point where the tendon enters the housing, there is provided a sealing joint for preventing the penetration of water and foreign bodies into a gap between the tendon and the housing. A plug is provided in the opposite end of the tubular assembly to protect grips and the ends of the tendons located therein. The opposite end of the tendon assembly is described as being left exposed to the environment.
In U.S. Pat. No. 4,348,844 issued to Morris Schupack et al on Sept. 14, 1982, there is disclosed another tendon assembly comprising a tendon enclosed in a sheath and suspended under tension between two spaced anchor members. The anchor members are entirely enclosed within an envelope or a housing. The sheath, the envelope and the housing are required to comprise electrically nonconductive materials for electrically isolating the tendon and anchor members from a surrounding concrete structure to thereby prevent the effects of corrosion caused by electrical currents.
The use of a housing or envelope which entirely encloses the anchor members in a tendon tensioning assembly as described above is expensive and if the protective housing must be installed as a separate unit in a structure, separate and apart from the anchor members, it is time consuming and costly to install. This is particularly true, since it has been found that in many structures there is little, if any, need to protect the entire anchor member or plate of a tendon assembly from corrosive elements so long as the exposed portions of the tendon itself are fully protected.